1. Field of the Invention
This invention relates to fan assemblies for motor vehicles and, more particularly, to a high output engine cooling fan assembly for a motor vehicle having an inner set of blades and an outer set of blades connected to each other and to a common hub.
2. Description of the Prior Art
The internal combustion engine of a motor vehicle is normally cooled by fluid circulated through a jacket surrounding the engine. The fluid, in turn, is cooled by circulation through a radiator which is exposed to the ambient air. When the vehicle is in motion, "ram air" is forced over the radiator by the forward movement of the vehicle. Because the engine may also operate when the vehicle is not in motion, however, some provision must be made to circulate air over the radiator during this time.
Thus, motor vehicles are typically equipped with an engine cooling fan. Conventional engine cooling fans operate at one or more discrete speeds, and have a single set of fixed blades which all have identical shapes and thicknesses. Any given fan construction, however, operates at maximum efficiency only at one particular vehicle speed. At other vehicle speeds, the fan limits the volume of air that could theoretically pass over the radiator. Furthermore, conventional automotive engine cooling fans have hub-to-tip ratios ranging from 0.4 to 0.7 because any smaller ratios may result in recirculation of air, which decreases the efficiency of the system. Given a maximum feasible tip diameter dictated by space constraints, therefore, the hub must generally have at least a certain minimum diameter.